In the modern world, cellular wireless service is an increasingly popular means of personal communication. An important feature of contemporary cellular networks is an ability to locate the geographical position of a mobile station. Location technology is important for various reasons. For example, as many people carry their cellular phone on their person, the location of a mobile station (i.e., a cellular phone) can be used as a proxy for locating the person in possession of the phone. Accordingly, cellular location technology was initially developed to assist emergency services. In particular, E911 mobile location technology is used by law enforcement, rescue services, and others who are authorized to use it.
The availability of location information to support E911 services has given rise to the development of many other location-based services. For instance, given the location of a mobile station, a service provider (e.g., a wireless cellular carrier or third party) can provide the user of an mobile station (e.g., a cellular phone, PDA, or other type of device communicating via a cellular wireless communication network) with a weather or traffic report in the user's vicinity. As another example, a service provider can report a list of services or establishments (e.g., restaurants, parks, theatres, etc.) in the user's vicinity. As still another example, a service provider can provide a mobile station user with a map of the user's location or with directions for travel between the user's location and another location. And as yet another example, knowing that a mobile station is operating in a particular location, a location-based service provider can send the mobile station a location-based message, such as an advertisement or coupon for a nearby establishment. Other location-based services exist currently or will be developed in the future as well.
Many techniques can be used to locate a mobile station. For example, a radio access network may locate a mobile station by (i) using mobile satellite positioning data (e.g., a global positioning system (GPS)), (ii) using the round trip delay between a mobile station and a network entity to perform triangulation, and/or (iii) monitoring handoff messages. These techniques may be employed alone or in combination. Further, other techniques now known or later developed may also be employed alone or in combination with the above mentioned techniques.
In one common arrangement, a mobile station may be operable to provide its location to network entities using GPS. To facilitate a mobile station's use of GPS, a mobile location system (MLS) may inform the mobile station which satellites to tune to, by providing the mobile station with “assistance data” that is indicative of the appropriate satellites (e.g., the frequencies or other parameters that the mobile station should use to tune to the satellites). As mobile stations often relocate, the MLS may periodically update the mobile station with fresh assistance data.
When a mobile station does not possess fresh assistance data (that is, the mobile station either does not yet have assistance data or the mobile station has stale assistance data), the mobile station's processing time for a location request is greater. Specifically, the mobile station acquires the necessary assistance data and may further process that data in order to extract from it the relevant parameters, which assist the mobile station in tuning to the appropriate satellites. Furthermore, there may be instances where a mobile station is unable to obtain satellite-based positioning data, and therefore is unable to respond to a location request with its location. In particular, a mobile station may be unable to receive satellite communications if the mobile station is currently located in a position where its view of the sky is blocked, or if the mobile station's GPS receiver is not working, or in other circumstances.
Generally, situations where a mobile station is unable to respond to a location request can reduce the efficiency of the location-determination process. In this situation, when the mobile station will not return the requested data to the MLS, it would better for the MLS to know that fact and to simply resort to alternative location techniques. In addition, inefficiencies can be magnified in a situation where the MLS receives a request to determine the locations of a group of mobile stations, as may happen for instance when a fleet tracking application seeks to track the location of multiple mobile stations disposed in trucks. Accordingly, improvements are desirable.